Cutting gemstones

Faceted gemstones reveal the inherent qualities of a mineral, such as colour (or lack of it), clarity, fire and brilliance, which might otherwise remain hidden.

The skill of the cutter is very important here and many different cuts have been devised to show a wide range of gemstones at their best.

The earliest of cuts was the cabochon - a simple, polished dome. This cut is still widely used today for translucent or opaque stones that rely for their impact on colour or surface effect. Turquoise, opal and moonstone are cut this way.

The historic rose cut and its extension, the drop-shaped briolette, return to fashion from time to time.

The modern round brilliant cut evolved from earlier brilliant cuts and was devised especially for diamonds, with 57 or 58 facets mathematically angled to optimise this stone's fire and brilliance. It also maximises the yield from an octahedral diamond crystal.

There are many modifications of the brilliant cut, such as oval, marquise, pear and heart shape and new fancy cuts continue to be developed.

The step cut (also called trap cut) and its adaptations are suitable for coloured stones with low dispersion (fire) since they emphasise body colour. This cut has a large table facet, surrounded by long, rectangular facets above and below the setting edge (girdle) of the stone. The outline may take a variety of geometric shapes - rectangular, square, triangular, kite-shaped and more.

Small, rectangular step cut stones, with fewer facets, are known as baguettes and are used in rings as shoulder stones for larger gems.

A truncated form of the step cut is the emerald cut, designed to eliminate damage to a gemstone's fragile corners. This cut is used extensively for emeralds (hence its name) which have a tendency to brittleness. It is sometimes used for diamonds, being a useful cut for flatter diamond crystals and macles (twinned crystals), and a variety of other stones.

New cuts continue to be invented and old ones improved upon, as cutting technology becomes more sophisticated. Computerised lasers are widely used for diamond cutting, being extremely precise and increasingly affordable.


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